1. Field of the Invention
The present invention relates to a counterflow heat exchanger. More particularly, it is concerned with the structure of a so-called total heat exchanger in which two fluids undergo countercurrent heat exchange and provide, not only exchange of sensible heat, but also latent heat exchange involving absorption and evaporation of moisture.
2. Description of the Prior Art
Heat exchangers have been widely used in buildings, etc. for treatment of the air brought in from the outside. The so-called total heat exchanger which provides not only sensible heat exchange but also latent heat exchange, by using a heat exchange material which permits absorption, evaporation and transmission of moisture, is a recent development and is considered to be a superior heat exchanger.
However, it has been considered difficult to design such a heat exchanger with counterflow, although various attempts have been made to produce such counterflow heat exchangers. Examples of prior art, counterflow total heat exchangers are disclosed in Japanese Patent Application Laid-Open Nos. 65887/1980 and 65888/1980 and Japanese Patent Application No. 80938/1980. These prior art heat exchangers of a counterflow type employ heat exchange units such as are shown in FIG. 1 (Prior Art).
The prior art heat exchange unit illustrated in FIG. 1 includes rectangular headers b connected to both ends of heat exchanging elements a. The headers b have openings extending across half their width as indicated as c and c', respectively, and closed end wall portions d and d'. Thus, a first fluid will pass through opening c, the tube side of heat exchange elements a and opening c' as indicated by arrows p and p', while a second fluid will pass as indicated by arrows q and q' around the exteriors of the heat exchange elements a (shell side).
In operation of the heat exchange element of FIG. 1 however, the flow of the fluid passing through the inside of the heat exchange members a is non-uniform, thus causing an increased pressure drop. For example, if the fluid flows by suction in the direction of arrow p', those heat exchange elements a on the side adjacent the opening c' will carry a larger amount of fluid passing therethrough, while a lesser amount of fluid will pass through those heat exchange elements a having openings facing the closed portion d'. Due to such an offset, the potential heat exchange capacity is not fully realized, and a large pressure drop occurs.
Further, when a large number of heat exchange units, each constructed as shown in FIG. 1, are assembled into a heat exchanger by superimposing them within a casing, it is necessary to use a large amount of an adhesive or sealant in order to attain air-tightness even if a central separation frame is provided within the casing, and thus assembly of such a heat exchanger is tedious.